This invention concerns improvements relating to ceramic candle filter arrangements.
Candle filters are employed for gas cleaning to remove particulates from gases, usually at elevated temperatures, the candles being formed of tubular ceramics material to withstand the high thermal stressing to which they are in use subjected. However, the ceramics material used in such a high temperature environment tends to be of a fragile nature and thus should only experience as minimal physical stress as possible in view of the cyclical thermal stressing which it undergoes in parallel by virtue of the cleaning mechanism.
Candle filters are usually cleaned by a reverse flow high pressure clean gas pulse which has the effect of discharging particles which have become arrested by the filter material. Conventionally, the filter candles are held in place in a tube plate which separates the particle-laden gas space from the filtered gas space in the filter housing. The candles are sealed into the tube plate by means of hollow hold-down weights suitably clamped in position thereover, each hollow weight forming a flow passage to the interior of the candle. The high pressure gas used as the cleaning medium is introduced to the weight by a pipe which terminates close to the open mouth of the hollow weight. In practice, it has been found that inter alia the dynamic forces of the gas pulse occasion movement of the candle and its associated weight, thus attenuating the force of the gas pulse and causing leaks with a resultant loss of efficacy and efficiency.
High pressure gas injected into the filter candle travels in a pressure wave along the candle and is reflected by the base of the candle to travel back along the candle interior. The reflected pressure wave then encounters the hollow weight, which incorporates a venturi, and causes it to move or bounce from its intended holding down position with the concomitant effect of impacting the top of the candle which, by virtue of its inherent fragility, is thereby weakened and breakage is accelerated. The same process will also allow the ceramic candle element to move and provide a leakage path for solid particles.